An instrument for measuring endometrial blood flow in the uterus, using two thermistor probes

An instrument was developed for continuous measurement of thermal conductance reflecting blood flow locally in the endometrium. The probe consists of two small thermistors, one sensing the tissue temperature, and the other working at 5 degrees C elevated temperature, sensing the heat loss caused by thermal conduction mainly due to the blood flow. The power needed to keep this temperature difference was recorded as a measure of flow. When the instrument was tested in model experiments, for measurement of flows at temperatures of 35 to 40 degrees C, stable recordings with high sensitivity were obtained and no influence of the surrounding temperature was observed. Recordings were also made in vivo in non-pregnant women by applying the instrument to the endometrium of the uterine fundus. Intrauterine pressure was recorded simultaneously. The blood flow recordings were stable over long periods in spite of changes in body temperature, but with fluctuations of up to 0.1 mW concomitant with uterine contractions. Pulse-syncronous variations in flow were recorded, indicating a high sensitivity and a short time constant of the instrument. The blood flow effects of vasoactive substances, i.e. vasopressin and a vasopressin antagonist, could readily be distinguished. It is concluded that this instrument can be used for semi-quantitative recordings of blood flow in cavities of the body, for example the uterus, which can be reached by small probes and that changes of body temperature do not effect the measurements.